It is customary to use porous polymer supports in separation methods as separating membrane. The transport of fluids across such membranes occurs by several mechanisms that depend on the structure and the nature of the porous support. The commonest membranes are synthetic or natural porous organic polymers. In these membranes the pores are interconnected and the solid matter represents only a small proportion of the total volume of the membrane. It is customary to modify the surface of these polymer supports by functionalization, or by low pressure plasma polymerization (less than 1,000 Pa).
The UIPAC nomenclature recognizes membranes for microfiltration (pore size greater than 50 mn), ultrafiltration (pore size between 2 nm and 50 nm), nanofiltration (pore size less than 2 nm), membranes for inverse osmosis (ultramicropore size less than 0.7 nm), and dialysis membranes that display characteristics close to some of the preceding categories (ultrafiltration, nanofiltration).
In photography, it is desirable to be able to regenerate photographic processing baths, especially of photographic developing agents. During the processing of exposed photographic products chemicals from the photographic products accumulate in the processing solutions. The presence of these compounds gradually lowers the efficiency of the bath.
In the case of a developing agent during the developing of silver halide photographic products, the developing bath becomes enriched in halide ions from the photographic product. When these ions are bromide or iodide, they considerably reduce the speed of the development of the image.
To avoid this problem, it is customary to replenish the bath by adding new developer, at the same time removing excess spent developer by overflow. The parameters of the replenishment are defined so as to maintain a halide concentration that will not adversely affect the efficiency of the developing bath.
With this method, it is necessary to adjust the bath replenishment parameters for each type of photographic product treated. In addition, it generates unwanted liquid photographic effluent.
For several years photographic bath treatment methods have been under development to recycle all or part of these seasoned baths. In the case of photographic developing agents, selective membranes have been used to remove bromide ions. For example patent application PCT/WO 9501541 describes a selective membrane with a hydrophobic surface obtained by sol-gel treatment from fluoroalkoxide.
To make continuous or discontinuous photographic bath replenishment efficient, it is necessary to extract those species that tend to reduce the efficiency of the bath, without modifying the other parameters of the processing bath, in particular, without modifying the concentration of any of the chemicals useful for the photographic development, the pH, etc. In particular it is most desirable to be able to control the water flow to avoid dilution of the processing bath.